The proposed research is a continuation of experimental work towards the long-range goals started two years ago. Our present specific research aims are based on the findings obtained during the initial grant period. The overall objective of this proposed research is twofold: 1) to establish at the ultrastructural level, the characteristics of the surface membrane of sporozoites of mammalian malaria, and II) to investigate the mode of parasite-host cell interaction, particularly the uptake of sporozoites by macrophages and their penetration into liver cells. Particular emphasis will be placed on the following aspects: a) characterization of the surface membrane of salivary gland sporozoites by freeze-fracture and etching techniques, b) characterization of the modifications of these membranes induced by antigenic maturation, and by the interaction of the parasites with antibodies, c) localization of glycoprotein receptors on the surface membrane of salivary gland sporozoites, d) clarification of the interaction between macrophages and sporozoites, in vitro, with emphasis on ingestion and/or penetration of sporozoites into macrophages, e) characterization of the role of the survival of normal serum-treated sporozoites within macrophages, and the degenerative changes of immune serum-treated sporozoites, and f) invasion of liver cells by sporozoites and their subsequent intracellular development in vitro.